/*
 * Copyright (C) 2012 Facebook, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.facebook.concurrency;

import java.util.Map;

/**
 * Subset of Map relevant to doing caching. Provides an iterator that allows removal of entries from
 * the cache
 *
 * @param <K> key to use in the cache
 * @param <V> value of the cache
 * @param <E> exception that may be thrown when creating the value for the cache
 */
public interface ConcurrentCache<K, V, E extends Exception>
    extends Iterable<Map.Entry<K, CallableSnapshot<V, E>>> {
  /**
   * Returns a value associated with the specified key, creating a new value if no previous mapping
   * existed.
   *
   * <p>NOTE: on exception, the exception will be cached as the result for all future gets(...) on
   * this key until this key is explicitly cleared with a call to remove(...) or removeIfError(...).
   *
   * @param key - key to use in the cache
   * @return - returns the value in the cache for the specified key, creating a new value if one did
   *     not previously exist
   * @throws E - user specified value creation exception
   */
  public V get(K key) throws E;

  /**
   * atomic insert that will replace any existing value
   *
   * @param key
   * @param value
   * @return existing value for key, or null if none is present
   * @throws E
   */
  public V put(K key, V value) throws E;

  /**
   * Removes the specified key from the cache, and returns the associated result, which may either
   * be a return value or a value creation exception.
   *
   * @param key - key to remove from the cache
   * @return removed entry, null if not present
   * @throws E - may throw a creation exception if the create failed, but will still remove the
   *     cached result
   */
  public V remove(K key) throws E;

  /**
   * Removes the key if the cached result is an exception
   *
   * @param key - key to remove from the cache
   * @return true iff the element was removed
   */
  public boolean removeIfError(K key);

  /**
   * This checks if there is a cached result associated with the key. If so, it returns a
   * CallableSnapshot, null otherwise
   *
   * @param key - key to check
   * @return CallableSnapshot or null if not present
   */
  public CallableSnapshot<V, E> getIfPresent(K key);

  /** Unconditional clear operation on the cache */
  public void clear();

  /** Optionally may apply heuristic to prune the cache. */
  public void prune() throws E;

  /** @return The number of keys stored in the map */
  public int size();
}
